It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.
Over the past 15 years, forced-air warming (FAW) has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket.
Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and bulkiness, which, at times, may obscure the view of the surgeon. Moreover, the low specific heat of air and the rapid loss of heat from air require that the temperature of the air, as it leaves the hose, be dangerously high—in some products as high as 45° C. This poses significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.
To overcome the aforementioned problems with FAW, several companies have developed electric warming blankets. However, these electric blankets have a number of inadequacies, for example, the risk of heat and pressure injuries that may be suffered by a patient improperly coming into contact with the electrical heating elements of these blankets. It is well established that heat and pressure applied to the skin can rapidly cause thermal injury to that skin. Such contact may arise if a patient inadvertently lies on an edge of a heated blanket, if a clinician improperly positions an anesthetized patient atop a portion of the heated blanket, or if a clinician tucks a heated edge of the blanket about the patient. Thus, there is a need for a heating blanket that effectively forms a cocoon about a patient, in order to provide maximum efficacy in heating, without posing the risk of burning the patient.
There is also a need for electrically heated blankets or pads that can be used safely and effectively to warm patients undergoing surgery or other medical treatments. These blankets need to be flexible in order to effectively drape over the patient (making excellent contact for conductive heat transfer and maximizing the area of the patient's skin receiving conductive as well as radiant heat transfer), and should incorporate means for precise temperature control.
Electric blankets are used to maintain a patient's body temperature in a wide variety of surgical procedures. The sterile surgical field in each procedure can be quite different, and electric blankets of varying sizes and shapes are needed in order to cover a maximum amount of body surface area surface outside the surgical field. For example, a blanket that only covers a lower abdomen and legs of a patient can be used during upper body surgeries. Similarly, a blanket that covers outstretched arms and a chest area of a patient is useful for patients undergoing lower body surgery.
Upper body warming blankets that drape across the arms and chest are useful but block access to the chest. Such access may be needed, such as for surgical site preparation or for access to EKG leads on the chest during surgery. In addition, the chest portion of such blankets can also rub against the patient's neck and chin, potentially causing patient discomfort. Furthermore, such blankets require that the patient's arms be extended at a 90 degree angle from the patient's body. This position may not always be preferred and the lack of adjustability or alternative positions may lead to discomfort for some patients. The maximum width of the heated portion of a standard warming blanket is also limited by the available space between the patients chin/neck and the upper edge of the surgical prep site and drapes. In small patients, or in cases where the surgical prep site extends up to or past the nipple line, the blanket must be very narrow, or it may end up extending up and over the patients face which is undesirable.
It may also be desirable that such upper body blankets be adaptable for placement over other body parts, such as the legs of the patients.
Accordingly, there remains a need for flexible heater subassemblies and blankets that effectively cover a desired amount of body surface in a variety of arm positions without rubbing against the chin or neck and without blocking access to the chest. Various embodiments of the invention described herein solve one or more of the problems discussed above.